As a device for driving a rotary machine such as a compressor, there is a device having an electric device that generates rotational driving force and a transmission device that changes the speed of the rotational driving force generated by the electric device and transmits the result to the rotary machine.
Patent Literature 1 discloses a device in which a constant speed electric motor and a variable speed electric motor for variable speed are used as an electric device and a planetary gear transmission device is used as a transmission device, in order to accurately control a gear ratio. In this device, it is possible to change the number of rotations (a rotational speed) of an output shaft of the transmission device connected to a rotary machine by changing the number of rotations of the variable speed electric motor.